The vKeyBoard mentioned on the Teensy project page seems to do exactly the USB-to-USB trick described above, but using two Teensy boards, which use an ATMega32U4 each. These chips might even provide a way to get the desired functionality in one chip by using vUSB to get a second USB port and optocouplers USB-side, but they are rather difficult to work with unless preassembled in a teensy.

Physical resources

We hope to be granted access to Metalab / WhateverLab resources for physically creating the boards (PCB etching (or milling?), solder station, parts repository / order collections), and will approach metalabbers as soon as we know what we want at all.